Process of manufacture of magnetic cores



g-l atented Oct. 19 29 m-mp sures PATENT, OFFICE FREDERICK JI'GIVEN, OI EAB'J, OmGE, JERSEY, ASSIGNORTO BELL TELEPHONE .LABOBATOBIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW You . r' or 'muirncrunn or menarro corms 80 Drawing.

This invention relates to magnetic material and particularly to the manufacture of magnetic dust cores from nickel-iron or other magnetic alloys.

An object of this invention is to provide a '5 method of manufacturing magnetic alloy nickel, iron and impurities must be careIully controlled,andintypical casesisheld t0 Witl1.

. dust cores having uniform characteristics.

A related ob]ect is to minimize waste in the teristics.

ln the manufacture of magnetic dust cores it is desirable that the cores have uniform characteristics such as uniform permeability, stability, eddy current losses and hysteresis two quantities as low as possible. To obtain the characteristics desired, the percentage of in 1%; or 2% of the prescribed composition. Also, if the annealing and insulating processes are not carried out within the required limits of deviation, the dust may not be within the stability requirementsa'nd'must be re-.

jected or usedfor'poorer grade" cores. The

' process of this invention increase'swthe number of permalloy dust coreshav ng satisfactory characteristics over the number 1manu-.

- ture has characteristics intermediate the characteristics of the original quantities. \It

has also been discovered that if acertainquam,

tity of permalloy dust having a negative stability characteristic is mechanically mixed with a quantity of permalloy dust having a positive stability characteristic, the resulting mixture has a stability characteristic between the characteristics of the original-quantities.

,These results were found to be true where the stability characteristicsof the original quantities were both positive and where the characteristics concerned. were the permeability and core losses of the material as well as manufacture of cores having such charac-.

losses. it is also desirable to have the ,last' Application in. February a, 1m.- Serial no. 338,050.

the stability. These findings form the basis of the present invention.

In the previous method of manufacturing permalloy dust. cores where the melts comprise nickel, iron and impurities in certain percentages, the composition is controlled as accurately as practicable when charging the furnace.- However, it is. practically mpossible, on a commercial basis, to make the com- 1 positions of the result-ing ingots from all melts identical, or always within the desired deviations from the prescribed composition. The ingots of each melt are analyzed, however, and the compositions noted. The ingots within the composition requirements are then ground into dust and the dust annealed, insulated and pressed into cores. The annealing of the dust is carried out in lots, each annealed lot being tested for permeability and stability by havinga sample core made up and tested. If the core is within the requirements the lot of dust from which the sample core was made proceeds in the manufacturing routine and results in. satisfactory cores. process results insatisfactory cores, the difli- 'culty of controlling-the composition of the al- While this loy within the required limits has resulted, in v the'past, inthe rejection of a large percentage ofthecore material, which represented a Waste sincethe material must be scrapped or else reworked. f

The present invention reduces this waste or the amount of .dust formerly rejected as being'unsatisfactory for high grade cores.

The invention in efiect extends the limits within which the composition of the ingots .may-be held andthe limits within which the characteristics of the annealed dust'may'be held, and still results in more uniform and higher grade average product than was obtained by prior art methods.

In one embodiment-of the invention and in accordance'with the discoveries outlined above, the dust from ingots having a low content of nickel is mixed with dust from ingots having a highcontent of nickel so that on reaching the annealing stage the composition is a mechanical mixture having an overall composition which is within the requiremetnts. This permits utilizing ingots having unsatisfactory compositions and compositions outside former requirements, providing therefrom a dust mixture which will make up into satisfactor cores. The ingots are analyzed and those liaving compositions which will make u intofirst grade cores are ground and sent t irough the routine process as mentioned above. However, those which will not make up into satisfactory cores are held back until ingots having compositions oppositely proportioned are found. These unsatisfactory ingotsare then ground and the dust therefrom mechanically mixed and sent through the routine process.

The next step is the annealing process which is accomplishedby placing a certain quantity or lot of dust in annealing pots and subjecting the dust to certain temperatures for certain periods of time. As mentioned hereinbefore with respect to holding the composition of the ingots to their optimum com-' position, it is also difii'cult on a commercial basis to control the elements affecting the annealing of the dust to always produce'a uniform anneal for all lots of dust. quently different lots of dust have difierent anneals and different characteristics. In the course of manufacture, according to prior art practice, each lot of annealed dust is placed in a separate bin for analysis, the analysis consisting of the making up of sample cores from each lot and testing these cores for their permeability, stability and core losses as mentioned above. The lots of dust which show b this test that they will make up into satis actory cores are ,then put through the remaining steps of the core manufacture such as insulating and pressing into rings or laminations from which the cores are built up.

In accordance with the present invention, however, the'lots of annealed dust which bythe old process would have been rejected, are now made into satisfactory cores. The lots which show a permeability or stability which is without the acceptable limits in one direc tion, are mechanically mixed with the lots which show a permeability or stability varying in the opposite direction from the mean. For instance, if the stability of the sample core from one lot gives a positive characteristic-of 5 and another sample core from a different lot gives a negative characteristic of 5, the mixm of the two lots of dust in equal parts wil? produce a core which will give theoretically a perfect stability characteristic. If a change of i2 is allowable then dustproduoing cores having a stability of zero to 6 may be mixed with dust producing cores having a stability of 4 and provide satisfactory cores. No objectionable effects are produced on the core losses when the permeability or-stability characteristics are regulated in this way. After the tests, the lots, according to their analyses are mechani- Consecally' mixed in proportion to their departures from the required analysis and sent through the remaining steps of the manufacturing process as outlined above.

.In the employment of the above described process, cores havin more uniform characteristics are obtaina le from a wider variation in both the composition of the original alloys and in the characteristics of the annealed dust.

What is claimed is: I

1. In the art of making magnetic cores of finely divided magnetic alloys, the method of securing a core of given magnetic characteristics from finelydivided alloy material which deviates in its characteristics from the characteristics to be obtained, comprising mechanically mixing together, proportionate parts of the finely divided core material whose characteristics deviate from the desired values, in relative quantities dependent upon the direction and extent of such deviations to produce a mixture having the re quired resultant characteristics;

2. A process of manufacturing magnetic dust cores comprising mechanically mixing a definite quantity of dust having one composition and an unsatisfactory characteristic in one direction with a quantity of dust having another compositionand an unsatisfactory characteristic in the opposite direction to obtain a satisfactory characteristic for the mixture. j

3.- A process definite composition and value of stability from grades of dust having unsatisfactory compositions and values of stability comprising mechanically mixing a certain quantity of said dust having an'unsatisfactory composition and value of stability in one direction with-a measured quantity of dust having a proportionate deviation in the opposite direction from said desired definite composition and value of stability.

4. A method of manufacturing magnetic dust cores having a definite composition and characteristics within certain limits comprising first, mechanically mixing a dust composition having too low a content of one comonent in one direction with a composition iiaving too high a content of said component in the OPPOSltG direction, and second, mechanically mixing one mixture of said dust having a oor characteristic in one direction with anot er mixture of said dust having a deviation from normal in said characteristic in the opposite direction.

5. A process of manufacturing a magnetic dust core havin a definite composition and characteristics rom nickel-iron alloys .hav-

of manufacturing magnetic dustcores from ironi-nickel alloys having a in different compositions comprising first rinding said alloys and mechanically mixmg the dust from said alloys having too high was: 4

) 'loys having too low a nickel content, and second, annealing said alloys in dustform .in definite lots and thirdmechanically mixing said lots'havin deviations from normal in r characteristics 1n one direction with said lots having deviations froni normal in the same characteristics in the o osite direction.

.7 In witness whereof hereunto subscribe my name this'30th day of J amiary 1929. m FREDERICK J. GIVEN. 

